The present invention relates to a belt apparatus for transporting a sheet and more particularly to a sheet transportation belt apparatus of the type in which a plurality of transportation belts are juxtaposed in the width direction of sheets to be transported, such as photosensitized paper, image transfer sheets, and original sheets in copying machines.
In diazo copying machines in which an original sheet to be copied and a photosensitized paper are superimposed and exposure is performed by passing the superimposed original sheet and photosensitized paper over a light source, a sheet transportation belt apparatus is usually employed for transporting the superimposed original sheet and photosensitized paper to an exposure station. Generally, the sheet transportation belt apparatus for use in such copying machines comprises a plurality of sheet transportation belts, which are juxtaposed and trained over a plurality of rollers, and an exposure cylinder, such as a glass cylinder having a light source therein, is disposed between the rollers in such manner that the other peripheral surface of the exposure cylinder is in pressure contact with the transportation belts, whereby an exposure area is formed in the contact portion between the exposure cylinder and the transportation belts, where the superimposed original sheet and photosensitized paper are tightly held for exposure.
In such apparatus, however, a uniform tension is not always applied to each transfer belt, and accordingly each transfer belt is not always in uniform pressure contact with the outer peripheral surface of the exposure cylinder due to the production errors of the transportation belts, the rollers for supporting the transportation belts, tension rollers and exposure cylinder. Under such circumstances, a force having a lateral component with respect to the superimposed original sheet and photosensitized paper is applied to the superimposed original sheet and photosensitized paper. As a result, the original sheet is shifted from the photosensitized paper and, in particular when the photosensitized paper is a roll paper, the paper may become wrinkled.